Move ui_test_utils::RunMessageLoop to test_utils so that it can be reused by content_browsertests.

chrome/browser/download/download_browsertest.cc

Index: chrome/browser/download/download_browsertest.cc
===================================================================
--- chrome/browser/download/download_browsertest.cc	(revision 148497)
+++ chrome/browser/download/download_browsertest.cc	(working copy)
@@ -122,7 +122,7 @@
     // Cannot complete immediately because the history backend runs on a
     // separate thread, so we can assume that the RunMessageLoop below will
     // be exited by the Quit in OnQueryDownloadsComplete.
-    ui_test_utils::RunMessageLoop();
+    content::RunMessageLoop();
   }
 
   bool GetDownloadsHistoryEntry(DownloadPersistentStoreInfo* result) {
@@ -1034,7 +1034,7 @@
       &download_assempted));
   ASSERT_TRUE(download_assempted);
   observer.WaitForObservation(
-      base::Bind(&ui_test_utils::RunMessageLoop),
+      base::Bind(&content::RunMessageLoop),
       base::Bind(&MessageLoop::Quit,
                  base::Unretained(MessageLoopForUI::current())));